Final answer:
Chemoresistance is the term used to describe the resistance of a tumor to chemotherapy. Due to the ability of cancer cells to mutate and develop resistance, treatment strategies often involve combination drug therapies.
Step-by-step explanation:
The resistance of a tumor to chemotherapy is known as chemoresistance. This phenomenon occurs when cancerous cells that are initially suppressed by a specific drug eventually develop a resistance to that drug. The challenge with cancer treatment is that there is not just one type of cancer, but potentially hundreds, each with slight variations. Cancerous tumors can easily mutate, causing them to become resistant to chemotherapy drugs. Therefore, treatment often requires a multi-drug approach to try to prevent or overcome this resistance. Effective cancer treatment may involve the use of several drugs in combination, and even then, drug resistance remains a significant hurdle.